Preparation Of Porous Carbon Nanofibers Using Dmso2as Pore-forming Agent Via Electrospinning Technology For Capacitive Desalination

With the rapid development of social economy, water resource has become the criticalstrategic issues for the sustainable development of mankind. Seawater and brackish waterdesalination, wastewater regeneration and gray water recycle can effectively relieve thecontradiction between supply and demand of water resource. Therefore, it’s significant to haveresearch on the seawater and brackish water desalination technology. Capacitive deionization(CDI) is a kind of emerging water desalination technology which holds the promise of obtainingpotable water. Compared with traditional desalination methods, CDI has a number of outstandingadvantages such as high water recovery, recyclable energy, low energy consumption, no secondarypollution and so on. As a consequence, it stands out in all kinds of desalination technology. Theperformance of capacitive deionization technology mainly depends on the properties of theelectrode material and the electrode materials with high specific surface area, suitable pore sizedistribution and proper surface functional groups are necessary for the CDI device. Due to the lowcost, high conductivity, high surface area and stable physical and chemical characteristics ofporous carbon materials, it is widely used as electrode materials. Because carbon nanofiber webwith good mechanical property can be used as the self-support electrode and it’s simple andversatile for the preparation of nanofiber using electrospinning technique, carbon fiber electrodeattracts intensive attention with the dramatic development of the electrospinning technology.Polyacrylonitrile (PAN) is generally used as an electrospinning material to produce pristinenanofibers due to the good spinnability and considerable carbon yield. However, pure PAN basedcarbon nanofibers display smooth surface, so the additional activation processes such as physicaland chemical post-treatment are often necessary to enhance the specific surface area of thenanofibers and ion adsorption capacity of the carbon fiber electrodes.The phase separation process is introduced to explore another way to fabricate thePAN-based porous carbon nanofiber in our work. Dimethyl sulfone (DMSO2) was added into the PAN solution as a pore forming agent. The PAN/DMSO2pristine nanofiber was obtained byelectrospinning. DMSO2was fixed in the fiber and phase separation occurred between PANsubstrate and DMSO2. In the subsequent preoxidation process, the porous nanofiber was obtainedbecause of the volatilization of DMSO2. The obtained porous carbon nanofiber web with highspecific surface area and suitable pore size distribution can be used directly as a free-standingelectrode material for CDI after high temperature carbonization.The fixed mass of DMSO2in fiber and fiber morphology influenced by the condition ofelectrospinning were studied. The pore structure of carbon fiber and the deionization amount ofthe corresponding electrode were investigated using the PCNFs fabricated by the solution withdifferent mass of DMSO2. The main results are as follows：The different amount of DMSO2was added into the PAN solution and stirred at roomtemperature to form the homogeneous precursor solution with various mass ratio of PAN toDMSO2. The PAN/DMSO2composite nanofiber was prepared by electrospinning. The mass ofDMSO2fixed in fiber increased with lower temperature and increased as increasing the amount ofDMSO2added in the precursor solution, as demonstrated by TG and FTIR. It was demonstratedthat DMSO2could be reused by the self-made setup.PCNFs was obtained after heat treatment without the need of an additional treatment. Thenitrogen adsorption test shown that the specific surface area of PCNFs increased firstly and thendecreased as increasing the amount of DMSO2. The pore size distribution of PCNFs wereobviously different. The CV measurement was carried out in different electrolyte concentrationand different scan rates using the PCNFs as the self-supported electrodes. The results displayedthat the specific capacitance of the PCNF increased with the increasing of DMSO2fixed in thefiber. The deionization performance of the PCNF electrodes fabricated from the PAN/DMSO2blend solution with the mass ratio of2/3was the best. The deionization amount was8.1mg/g andthe current efficiency was61%. The PCNF electrodes are very stable and it’s a promisingelectrode material.